skip to main content

Title: Multiple pathway quantum beat spectroscopy
We investigate quantum beats by monitoring cooperative emission from rubidium vapor and demonstrate correlated beats via coupled emission channels. We develop a theoretical model, and our simulations are in good agreement with experimental results. The results pave the way for advanced techniques measuring interactions between atoms that are excited to high energy levels.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Frontiers in Physics
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Quantum coherences, observed as time-dependent beats in ultrafast spectroscopic experiments, arise when light–matter interactions prepare systems in superpositions of states with differing energy and fixed phase across the ensemble. Such coherences have been observed in photosynthetic systems following ultrafast laser excitation, but what these coherences imply about the underlying energy transfer dynamics remains subject to debate. Recent work showed that redox conditions tune vibronic coupling in the Fenna–Matthews–Olson (FMO) pigment–protein complex in green sulfur bacteria, raising the question of whether redox conditions may also affect the long-lived (>100 fs) quantum coherences observed in this complex. In this work, we perform ultrafast two-dimensional electronic spectroscopy measurements on the FMO complex under both oxidizing and reducing conditions. We observe that many excited-state coherences are exclusively present in reducing conditions and are absent or attenuated in oxidizing conditions. Reducing conditions mimic the natural conditions of the complex more closely. Further, the presence of these coherences correlates with the vibronic coupling that produces faster, more efficient energy transfer through the complex under reducing conditions. The growth of coherences across the waiting time and the number of beating frequencies across hundreds of wavenumbers in the power spectra suggest that the beats are excited-state coherences with a mostly vibrational character whose phase relationship is maintained through the energy transfer process. Our results suggest that excitonic energy transfer proceeds through a coherent mechanism in this complex and that the coherences may provide a tool to disentangle coherent relaxation from energy transfer driven by stochastic environmental fluctuations. 
    more » « less
  2. Given the challenges of wayfinding in large indoor built environments, especially for persons with disabilities (PWDs), a new class of accessible technologies called built environment accessible technologies (BEAT) are being developed. Such technologies are envisioned to help achieve product and opportunity parity for PWDs. The impact and adoption of these BEATs depends largely on clear and quantifiable (tangible and intangible) economic benefits accrued to the end-users and stakeholders. This paper describes the results of a survey conducted to measure potential benefits in terms of quality of life and quality of work life (work productivity) by increased accessibility provisions within built environments as it relates to navigation for PWDs and those without disabilities. Results of this work indicate that BEATs have the greatest potential to improve mobility and exploratory activities for people with disabilities, exploratory activities for people without disabilities, and improve job security for everyone. 
    more » « less
  3. null (Ed.)
    We study ranked enumeration of join-query results according to very general orders defined by selective dioids. Our main contribution is a framework for ranked enumeration over a class of dynamic programming problems that generalizes seemingly different problems that had been studied in isolation. To this end, we extend classic algorithms that find the k -shortest paths in a weighted graph. For full conjunctive queries, including cyclic ones, our approach is optimal in terms of the time to return the top result and the delay between results. These optimality properties are derived for the widely used notion of data complexity, which treats query size as a constant. By performing a careful cost analysis, we are able to uncover a previously unknown tradeoff between two incomparable enumeration approaches: one has lower complexity when the number of returned results is small, the other when the number is very large. We theoretically and empirically demonstrate the superiority of our techniques over batch algorithms, which produce the full result and then sort it. Our technique is not only faster for returning the first few results, but on some inputs beats the batch algorithm even when all results are produced. 
    more » « less
  4. Abstract

    Heart rhythm assessment is indispensable in diagnosis and management of many cardiac conditions and to study heart rate variability in healthy individuals. We present a proof-of-concept system for acquiring individual heart beats using smart speakers in a fully contact-free manner. Our algorithms transform the smart speaker into a short-range active sonar system and measure heart rate and inter-beat intervals (R-R intervals) for both regular and irregular rhythms. The smart speaker emits inaudible 18–22 kHz sound and receives echoes reflected from the human body that encode sub-mm displacements due to heart beats. We conducted a clinical study with both healthy participants and hospitalized cardiac patients with diverse structural and arrhythmic cardiac abnormalities including atrial fibrillation, flutter and congestive heart failure. Compared to electrocardiogram (ECG) data, our system computed R-R intervals for healthy participants with a median error of 28 ms over 12,280 heart beats and a correlation coefficient of 0.929. For hospitalized cardiac patients, the median error was 30 ms over 5639 heart beats with a correlation coefficient of 0.901. The increasing adoption of smart speakers in hospitals and homes may provide a means to realize the potential of our non-contact cardiac rhythm monitoring system for monitoring of contagious or quarantined patients, skin sensitive patients and in telemedicine settings.

    more » « less
  5. null (Ed.)
    The dive response, a decrease in heart rate (ƒH) and peripheral vasoconstriction, is the key mechanism allowing breath-hold divers to perform long duration dives. This pronounced cardiovascular response to diving has been investigated intensely in pinnipeds, but comparatively little is known for cetaceans, in particular in ecologically relevant settings. Here we studied the dive ƒH response in one the smallest cetaceans, the harbour porpoise (Phocoena phocoena). We used a novel multi-sensor data logger to record dive behaviour, ƒH, ventilations and feeding events in three trained porpoises, providing the first evaluation of cetacean ƒH regulation while performing a variety of natural behaviours, including prey capture. We predicted that tagged harbour porpoises would exhibit a decrease in ƒH in all dives, but the degree of bradycardia would be influenced by dive duration and activity, i.e., the dive ƒH response will be exercise modulated. In all dives, ƒH decreased compared to surface rates by at least 50% (mean maximum surface=173 beats min−1, mean minimum dive=50 beats min−1); however, dive ƒH was approximately 10 beats min−1 higher in active dives due to a slower decrease in ƒH and more variable ƒH during pursuit of prey. We show that porpoises exhibit the typical breath-hold diver bradycardia during aerobic dives and that the heart rate response is modulated by exercise and dive duration; however, other variables such as expectations and individual differences are equally important in determining diving heart rate. 
    more » « less